There are two major passive methods for insect control: traps and toxic baits. Both types must incorporate some kind of insect attracting material in order to be effective. Food materials are often used as the insect attracting material. An example of a material attractive to wasps is U.S. Pat. No. 4,851,218 to Hildebrandt et al., "Method for Controlling Insects of the Family Vespidae Utilizing Interspecific Bait". Traps, whether of the sugar water in a bottle variety or the flypaper variety, are only effective on individual insects. Toxicant preparations can be formulated with different types of pesticides. Pesticides can be used in two major ways, for quick-kill or for so-called "delayed-kill."
Quick-kill pesticides which kill shortly after contact or ingestion, are desirable for control of populations of insects of non-aggregating behavior. Quick-kill pesticides are usually used as aerosol and spray insecticides which may be dispersed or formulated in aqueous, non-aqueous or partially aqueous systems for ease of dispensing.
Pesticides which have a "delayed kill action" are most useful for a different type of insect: the so-called social insect. "Delayed-kill" pesticides can derive their delayed kill action from intrinsic properties of the chemical, if the toxic moiety of the compound itself has a delayed release. Membrane barriers, microencapsulation, or even binding of the pesticide to a polymer substrate, have been used as methods for accomplishing this delayed release. "Delayed kill" pesticides can also be of the type that are not delayed release, but disrupt an insect's internal system. Disruption of certain internal systems will cause the insect to succumb after a period of days. A different type of "delayed kill" is obtained from a concentration dependent toxicant, which, at higher concentrations, would provide a quick-kill and at lower concentrations would not kill immediately. Such a toxicant, however, has a "delayed action kill" effect as the target insect is killed as a result of repeated consumption of the toxicant.
The social insects include such species as ants, termites, wasps and bees. (Wasps and bees include both social and non-social types.) Social insects by definition have a social hierarchy, with workers and foragers, males, and an egg-laying queen. Quick kill of individual forager insects does not affect the main colony. However, if a "delayed action" toxicant is mixed with an insect attracting ingredient, the foragers will carry the toxicant-attractant formulation back to the home colony where it is shared by larvae, workers, and queen. If sufficient toxicant is transported back into the nest, it is possible to eradicate the entire colony by trophallaxis (a mutual exchange of food) within a week or two, (if the toxicant is sufficiently effective in the amounts that reach the colony). In order to assure that sufficient toxicant is carried back to the nest, the toxicant-attractant formulation must not be repellent to the pest and must be protected from degradation.
Wasps, which include such insects as yellowjackets and hornets, as well as those commonly called wasps, were considered, in the Old Testament, to be a plague upon mankind. Not only do wasps sting, sometimes with fatal results, but they also cause damage to fruit crops and they kill honeybees. Probably the greatest problem presented to man by wasps, however, is their nuisance value. They often are present in large numbers around recreational sites or garbage dumps or similar sources of available food. Thus effective methods of control are desirable.
The use and importance of "delayed action" pesticides for the control of social insects is known in the art.
Historically it has been found that the most effective method of wasp control is the destruction of the home colony. However, the main drawback with this direct approach is the difficulty in locating the home colony.
Various species of wasps and hornets may have nests that are subterranean, within the structure of homes, or "aerial" (in trees, under roofs, etc.). A problem in eradicating the home colony for all three types is, as stated, locating the home colony. The second type especially presents an access problem: it is difficult to introduce an effective amount of a toxicant into a nest within an existing home since precautions to protect those living there are necessary.
U.S. Pat. No. 4,540,711 to Bettarini et al, "Method for Combatting Infestations of Insects and Acari and Compositions for Use in Said Method", discloses the use of a hydroaquinone diether in an insect attracting ingredient for control of ants, especially fire ants. The use of the compound for termite control is also suggested, since it is effective against termites and they are also social insects. The patent also points out that such poisoned insect attracting ingredient must still be appetizing to the ants, or it will not be eaten or carried back to the nest.
Another "delayed action" toxicant for termite control is disclosed in U.S. Pat. No. 4,582,901 to Prestwich, "Fluorinated Cellulose Esters and the Use Thereof as Termiticidal Compositions". This patent clearly states the need for "delayed action" toxicants for termite control:
For a pesticide to be effective against termites and related pests it may have a somewhat delayed onset of activity. Termites typically feast upon a food supply and then return to their nest and regurgitate the food to be shared by those occupying the nest. Thus, a pesticide which instantly destroys the feeding termites has absolutely no effect upon those hatching on the nest. While the feeding termites are affected, those in the nest continue to multiply and thus the infestation remains.
The same considerations apply to any other type of social insect, and the Bettarini et al. patent similarly but not as completely discussed the "spreading action of delayed action toxicants".
The problems associated with the presence of wasps, especially around food processing and packaging plants, and the successful use of a delayed action chlorinated hydrocarbon insecticide for wasp colony destruction has been reported in Great Britain. ("Control of Wasps in Food Factories," Frank Jefkins, Food Trade Review, May 1961, p. 47). This solid insect attracting ingredient has been sold under the name Waspex. Wasp toxicant-attractant formulations can also be prepared and dispensed in the form of gels, syrups or liquids.
Since the insect attracting ingredient carrier for any "delayed action" toxicant formulation must be appetizing and non-repelling to the target insects, different insect attracting ingredients and different types of toxicant formulations must be used for different species.
Carbohydrate insect attracting ingredients are more generally acceptable than protein based insect attracting ingredients to wasps. Carbohydrates combined with small amounts of protein are also acceptable. Protein insect attracting ingredients are preferred by certain scavenging species. Protein insect attracting ingredients such as fish, chicken, etc., are highly susceptible to spoilage. Although antimicrobials and/or preservatives can prevent spoilage of protein insect attracting ingredients to some extent, these additives were found to be repellent to wasps. Many toxicants added to a insect attracting ingredient are unstable (decompose) in sunlight or air over a period of time making the toxicant-attractant formulation less effective. Toxicant decomposition products are often repellent to wasps and render the insect attracting ingredients unacceptable. Certain stabilizing agents such as antioxidants and surfactants can be used to stabilize the toxicants to some extent. However most of these additives tend to be repellent to wasps.
Aqueous insecticidal formulations are preferable to solid insecticidal formulations because a wasp must first cut a solid insect attracting ingredient into a piece of manageable size, then transport the piece back to the nest. The time and energy required to imbibe liquid toxicant-attractant formulation is less than is required to cut up the solid toxicant-attractant formulation. Thus, although transport times are the same, more toxicant is delivered to the nest per unit of time with liquids than with solids. Aqueous insecticidal formulations also have the advantage that they can satisfy the colony's need for water. For these reasons a stable water soluble toxicant is preferred.
Frequently used "delayed action" toxicants such as bendiocarb (2,2-dimethyl-1,3-benzodioxol-4-yl methyl carbamate) and Dursban (0,0-Diethyl-0-[3,5,6-trichloro-2-pyridyl]-phosphorothioate) are not water soluble and must be made water dispersible by the use of surfactants, organic solvents, and/or hydrotropes. The addition of such compounds to an aqueous insecticidal formulation, however, makes the formulation unattractive or even repellent to wasps. Another drawback of the dispersed or emulsified insecticide is that it can undergo phase separation in storage. The problem of such phase separation is that the insecticide will separate into the oil phase at the top, which will create inadequate and disproportionate delivery of toxicant-attractant formulation in the aqueous phase.
Although other "delayed action" toxicants such as Dipterex (dimethyl [2,2,2-trichloro-1-hydroxy ethyl]phosphonate), acephate (O,S-dimethyl acetylphosphoramidothioate) and borax are water soluble, it was found that the toxicant-attractant formulation prepared using these were not very attractive to wasps.
A further consideration for an effective "delayed action" toxicant is a careful balancing of the concentration and the kill effect. Too great a concentration of the pesticide will repel wasps and will produce too quick a kill for effectiveness in eradication of the home colony. A smaller concentration of toxicant allows a wasp to make repeated visits to the source of the toxicant-attractant formulation. After each visit, the wasp returns home, carrying some of the toxicant with it. The cumulative effect of the toxicant destroys the home colony, an effect that does not occur if the initial kill is too quick.
The fluorinated sulfonamides have been found to be effective "delayed action" insecticides for such social arthropods as ants. This is discussed in Ch. 21, Fluorinated Sulfonamides, in Synthesis and Chemistry of Agrochemicals, Vander Meer et al., (American Chemical Society, Washington, D.C., 1987). However, since such compounds are of limited solubility in water, they cannot be used with aqueous insect attracting ingredient components.
The Vander Meer et al. chapter also stated that perfluorooctane sulfonic acid form and its potassium salt provided good delayed activity on ants. The use of various amides of perfluoro compounds for the control of arthropods is disclosed by U.S. Pat. No. 4,921,696 to Vander Meer et al.
U.S. Pat. No. 4,092,110 to Adolphi et al. discloses the use of compounds of the formula C.sub.n F.sub.2n+1 SO.sub.3 M where n is an integer from 1 to 14 and M is hydrogen or a cation for treatment of wood or wood based materials from "animal pests," especially termites.